This invention relates generally to an improved low pressure mercury vapor discharge lamp of the fluorescent type having a particular type phosphor coating to emit skin tanning radiation when excited by ultraviolet radiation generated from the mercury vapor discharge. More particularly, the present type lamp construction provides satisfactory skin tanning with radiation in the UVA spectral region (320-400 nanometers wavelength) and which may further desirably include a phosphor combination providing preselected amounts of radiation in the UVB spectral region (280-320 nanometers wavelength) for additional skin tanning benefit.
Lamps of the fluorescent type to produce artificial skin tanning have been known for some time. The early lamps of this type utilized a coating of a single phosphor material to emit ultraviolet radiation in the approximate wavelength region 320-400 nanometers which produced artificial skin tanning without occasioning skin reddening (erythema) to any significant degree. A more recently introduced fluorescent lamp of this type generates both UVA and UVB radiation to promote more effective artificial skin tanning without further occasioning undesirable erythemal effects. Said improved fluorescent lamp of this type is described in U.S. patent application No. 72,958, filed Sept. 6, 1979, and assigned to the present assignee wherein the desired objective is achieved with a phosphor combination of a first phosphor emitting in the 320-400 nanometer region of the spectrum with a second phosphor emitting in the 280-320 nanometer region in the spectrum and which can be utilized as a blended mixture. A preferred phosphor material efficiently generating the desired UVB radiation is a lead-activated barium zinc silicate phosphor such as BaZn.sub.2 Si.sub.2 O.sub.7 :Pb which is disclosed in U.S. Pat. No. 2,846,403, issued to Hoekstra and Clasens. A suitable phosphor material efficiently generating UVA radiation can be europium-activated strontium borate such as disclosed in U.S. Pat. No. 3,431,215.
All of the above type skin tanning fluorescent lamps produce blue color visible emission, however, attributable to strong mercury discharge lines in the visible region at wavelengths of approximately 405, 436, 546 and 578 nanometers wavelength. Such blue color lamp emission is objectionable from the standpoint of color rendition to the lamp users. Thus, skin tones as well as clothing worn by a person while exposed to the lamp emission have an unflattering appearance which is undesirable. It would thereby be of benefit to modify the lamp color emission in a manner to improve the color rendition and especially without significant loss of the skin tanning effect otherwise produced with a conventional lamp. It would also be desirable to improve the color rendition of said skin tanning fluorescent lamps without requiring structural modification in the lamp design or additional modification to the apparatus now employing the conventional lamps.